Conventionally, fuse elements blown by self-generated heat when a rate-exceeding current flows are used to interrupt a current path. Examples of commonly used fuse elements include holder-fixed fuses having solder enclosed in glass, chip fuses having an Ag electrode printed on a ceramic substrate surface, and screw-in or insertable fuses having a copper electrode with a narrow portion assembled into a plastic case.
However, problems have been identified in existing fuse elements described above such as inability to surface mount using reflow, low current ratings, and inferior blowout speeds when increasing size for higher current ratings.
Moreover, in the case of a reflow-mountable rapid-interruption fuse device, in general, this would preferably have a high melting point Pb solder with a melting point of 300° C. or more in the fuse element in view of blowout properties. However, use of solder containing Pb is limited with few exceptions under the RoHS directive, and demand for a transition to Pb-free products is expected to rise.
Due to such demand, as illustrated in FIG. 16, a fuse element 100 is used in which a low melting point metal layer 101 such as of Pb-free solder and a high melting point metal layer 102 such as of silver or copper are laminated. Such a fuse element 100 having excellent mounting properties enabling surface mounting in fuse devices and protective devices using reflow is applicable to increased ratings and high-currents due to being covered by a high melting point metal, and can rapidly interrupt a current path by an erosive action of the low melting point metal on the high melting point metal during blowout.
Such a fuse element 100 can be manufactured, for example, by forming a film of high melting point metal 102 such as Ag using film-forming techniques such as plating, vapor deposition, or sputtering on the surface of an elongated low melting point metal layer 101 such as a solder foil.